To draw a shaded triangle from [0,0] to [100,32], define a TRIVERTEX structure with three elements and a single GRADIENT_TRIANGLE structure. The following example shows a GRADIENT_FILL_TRIANGLE call.
TRIVERTEX vert [4] ;
GRADIENT_TRIANGLE gTri;
vert [0] .x = 0;
vert [0] .y = 0;
vert [0] .Red = 0x0000;
vert [0] .Green = 0x0000;
vert [0] .Blue = 0x0000;
vert [0] .Alpha = 0x0000;
vert [1] .x = 100;
vert [1] .y = 0;
vert [1] .Red = 0x0000;
vert [1] .Green = 0x0000;
vert [1] .Blue = 0xff00;
vert [1] .Alpha = 0x0000;
vert [2] .x = 100;
vert [2] .y = 32;
vert [2] .Red = 0x0000;
vert [2] .Green = 0x0000;
vert [2] .Blue = 0xff00;
vert [2] .Alpha = 0x0000;
vert [3] .x = 0;
vert [3] .y = 32;
vert [3] .Red = 0xff00;
vert [3] .Green = 0xff00;
vert [3] .Blue = 0xff00;
vert [3] .Alpha = 0x0000;
gTRi[0].Vertex1 = 0
gTRi[0].Vertex2 = 1
gTRi[0].Vertex3 = 2
gTRi[1].Vertex1 = 0
gTRi[1].Vertex2 = 2
gTRi[1].Vertex3 = 3
GradientFill(hdc,vert,4,&gTRI,1,GRADIENT_FILL_TRIANGLE);